1. Field of the Invention
This invention relates to an improved adhesive composition for rigid PVC (polyvinylchloride) elements and more especially to a material which, despite a significantly reduced tendency towards stress-induced corrosion, even in critical applications, still satisfies current requirements with regard to storage life, conformity with industrial standards, creep strength, and gap-filling ability.
2. Statement of Related Art
For bonding rigid PVC elements such as molded PVC piping, construction elements, etc., it is common practice to use adhesive compositions which contain powder-form PVC dissolved in a suitable PVC solvent or solvent system. Characteristic application properties of adhesive systems such as these, such as working life and swelling behavior, may be regulated as required through the choice of the solvent mixtures.
The bondingf principle is based on the swelling, dissolving and diffusing powder of the solvents. The solvents diffuse into the underlying material, causing it to swell, and, in conjunction with the PVC introduced in solution, establish the bond when the adherend and substrate are pressed together. The solvents desorb over a period of time which cannot be exactly defined, so that a homogeneous bond is obtained.
Systematic investigations have shown that, because of their dissolving, evaporating and plasticizing properties, the solvents present in adhesives of the type in question have a different effect on possible structural damage arising out of the bonds. This becomes particularly critical when, in the case of heavily stressed moldings such as 4-way pipe fittings, the mechanical load applied is accompanied by additional accumulations of adhesive through displacement of excess adhesive applied between overlaying inner and outer sleeves.